Globaliser

Presumably all of this relates to the certification testing?

If so, are there significant differences from the routine RTO testing done on production aircraft as part of their pre-delivery testing, such as in the video posted by KeaneJohn?

Waterhorse

Globaliser

Thanks!

BertieBadger

Many thanks Steve_ZA, I had heard of Dave Wallsworth before, but not being a social media person, hadn't really come across too much of his stuff, that blog looks fascinating.

Thanks also to Waterhorse for the more specific answers, very interesting stuff - if I could just follow up on one point (and this may be a very naive question!):

Does this imply that when you land, you are always targeting a specific exit from the runway? And following from that - if the aircraft touches down further along (for whatever reason) - you simply brake harder? I'm not a particularly frequent flier by FF standards, probably 50 sectors a year on average - but it does seem that way from the cabin. Sometimes it's a fairly graceful deceleration, other times a bit more visceral, with harder braking sometimes coming later on - I'm guessing this is the pilot adjusting speed to make a given exit?

As a corollary, does there come a point where if you touch down particularly late, you just accept you will miss an exit rather than brake so hard it would cause passenger discomfort? Would that be an example of where the A320 pilot would be demonstrating their skills, to get it down early and produce a passenger-pleasing (and brake-preserving) gentle braking?

Thanks

All She Wrote

During briefing pilots will talk about where to exit the runway. Landing calculations can be done to determine which level of auto brake is used, some people (such as myself) prefer to select LO then do a manual over-ride as it's much more comfortable for the passengers than using Medium. Some people struggle more than others with high speed manual braking and end up delivering asymmetric braking (very common in higher crosswinds too as they end up keeping the centreline with asymmetric braking rather than the rudder), and thus elect to let the auto brake do its thing instead. The hardest braking can only be achieved by maximum reverse and manual braking, the most you'll usually be subject to as a passenger when flying somewhere with a smaller runway is medium autobrake and maximum reverse. I'd certainly rather miss an exit and exit further down the line than slam on the anchors when it isn't necessary. That said, unless one significantly misses the touchdown zone aiming point or is landing 5-10kts above the vapp used in calculations (for example flap 3 in icing conditions) there's no reason to miss the exit.

When you're experiencing harder braking later on it usually means they've decided LO won't be sufficient and done a manual override to make an exit. Different airlines almost certainly have different SOPs here.

BertieBadger

Many thanks All She Wrote, most instructive. (And again to Steve_ZA, Waterhorse, for some reason the system is not accepting my "like" on those posts)

G-BUSI

<br /><br />Shift + F5 while on the page to clear your cache for the page and then you can start liking posts again, need to do this constantly to like posts.<br />OT sorry!

Waterhorse

We always plan a landing to vacate at a particular exit. We are limited to a couple of auto brake settings and a couple of flap settings, the real difference can be in the runway state. You are probably aware that you need a little extra braking distance in the wet when driving, the same applies with an aircraft. Also the build up of rubber deposits from landing traffic can get slippery when wet. So we take these conditions into account and plan to vacate at a certain exit. At LHR they like us off ASAP, so dependent on the runway and the aircraft weight and the weather conditions will determine our braking plan. Other airfields may not need us off quite so soon so a different braking strategy will be used.

In in terms of significant threats to modern aviation a runway overrrun is right up there. BA prefer us to always use some level of predetermined braking, as most overruns statistically happen in daylight, CAVOK conditions on a long runway, so we are encouraged in these conditions particularly to use some level of autobraking. A classic for this sort of trap would be runway 16L at FCO, where rolling long can save quite a few minutes of taxing.

Sometimes the architects just just didn’t get it right and the exits are in the wrong place so we have to alter the braking and do it manually, this is where lead foot Larry the pilot let’s you know he’s doing some of that pilots stuff and you get the more sudden and sharp braking.

Oddly enough passenger comfort is not high on the priority list at these times, a safe landing is more important. Indeed a gentle touch down is not necessarily a good landing. A good landing is one in the right place, a and the right speed, inside the limits of the aircrafts landing gear. A smooth touchdown outside the touchdown zone would not be a good landing. Same sort of idea for braking, so long as it’s even and keeps the aircraft on the runway, vacating at a suitable point at a suitable speed it’s okay. IF we achieve a smooth touchdown with gentle and even braking to vacate the runway at the perfect place then the gods have smiled on us and we will all claim that was what we intended all along.

All She Wrote

BertieBadger

Thanks again Waterhorse,

This caught my eye

Now, admittedly I had to Google CAVOK But I've commented before that it's only natural that technical endeavours use their own jargon for various reasons, so given you guys and gals kindly take the time to answer our queries, I think that's entirely fair! But assuming it means "Cloud And Visibility OK", this has surprised me somewhat. To the non-pilot layman, what you've described would seem to be - well - "good conditions" for want of a better description, so it seems initially counter intuitive that these would be conditions correlated to overruns? Is it that pilots would routinely be doing manual landings under these conditions, and that this contributes somehow?

I hadn't even considered this aspect! - I don't know what technological progress has been made on aircraft braking, but while I expect it's fundamentally the same, i.e. push a friction material against a big disc, it's also possible/likely that there have been improvements in those materials, newer anti-lock controllers, tyre materials and design and so forth, so I wonder if someone sat down to design an airport today, would the exit layouts be different from 40 years ago to account for such advances?

Thanks again for your input, I know I'm not the only one here with an interest in the more technical/geeky side of things, so hopefully others find it equally interesting.

rapidex

I think RTO might give you the maximum braking. I accept this is not in the landing phase though.

Waterhorse

Sorry about the CAVOK - it is as you describe, good visibility and no low cloud. It is exactly because it is counterintuitive that I mentioned it. In terms of safety management, what we call CRM, it is the under arousal state that is the issue, the “it’s okay, I have a long runway and good braking conditions so I don’t need to worry about braking” which is okay until you have pushed yourself into a corner where you have run out of distance, braking ability and ideas.

The comment about architects was a little tongue in cheek, it’s just that some days with some turn off positions you simply cannot get a flap setting and brake setting that will work without any intervention. Pilots are lazy beasts, we like technology and gadgets. Having to brake for yourself is soooo 1990s.

Jumbodriver

Max manual is more than RTO in everything I've flown.

Generally the way to disconnect the autobrake is to apply more pressure than it to the brake pedals, if you couldn't apply more pressure (because RTO was max) then you'd never be able to disconnect it in the normal way.

Ancient Observer

Thanks to all for taking the time and trouble to reply to our questions! Much appreciated.

All She Wrote